Artificial SEI material and preparation method thereof, artificial SEI membrane and artificial SEI membrane modified negative electrode

Abstract

The invention discloses an artificial SEI material and a preparation method thereof, an artificial SEI film and an artificial SEI film modified negative electrode. The artificial SEI material is an organic polymer brush (CNF-g-PSSX) prepared by grafting cellulose nanofibers with polystyrene sulfonate. The polymer brush is of a crystal structure and has a firm framework; and the side chain of polystyrene sulfonate has rich-SO3 functional groups which are matched with cations in sulfonate, so that a rapid ion transmission channel is provided, high-current-density circulation can be realized, and good interface contact is ensured. Due to a special molecular topological structure and a multi-component synergistic effect, when the organic polymer brush forms an artificial SEI film, high mechanical strength, high ionic conductivity and low interface impedance can be obtained at the same time, and through strong electrostatic repulsion between a negatively charged-SO3 group and the surface of a negatively charged lithium dendrite tip, the electrochemical performance of the artificial SEI film is improved. An obvious inhibition effect is shown on the continuous growth of dendritic crystals.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery materials, and in particular to an artificial SEI material and a preparation method thereof, an artificial SEI film and an artificial SEI film-modified negative electrode. Background Art

[0002] Lithium-ion batteries (LIBs) are widely used in products such as consumer electronics (3C), electric vehicles, and power tools due to their high energy density, lack of memory effect, long cycle life, environmental friendliness, and adaptability to various environments. The rapidly growing power demands of these products are placing higher demands on the energy output of LIBs. Silicon (Si) is considered a promising candidate for high-energy anodes (negative electrodes) due to its superior theoretical capacity. However, in practical applications, the alloying reaction between Si and Li often leads to large volume expansion, which in turn causes the anode structure to shatter and the continuous formation of a solid electrolyte interface (SEI) on the surface of Si particles. Furthermore, the continuous consumption of lithium leads to a decrease in capacity during the lithiation / delithiation process. Furthermore, the expansion properties of Si-based materials, which cause lithium dendrite growth, also hinder the practical application of Si-based anodes. Lithium dendrites, resulting from the high activity of lithium during repeated insertion and deintercalation, can emerge from the anode surface, causing severe capacity loss and even piercing the separator, leading to increased self-discharge and even short circuiting.

[0003] The solid electrolyte interface (SEI) film plays a vital role in the stability and cyclability of lithium metal anodes. The SEI film is formed by the reaction of lithium and liquid electrolyte and is the interphase layer between the anode and the electrolyte. However, the SEI film is usually fragile and uneven, which can lead to uneven lithium ion flow and insertion. In addition, the mechanical stress generated by the huge volume expansion of silicon-based materials may also tear the SEI film layer, causing more lithium to be exposed to the electrolyte and further reaction. When lithium ions flow through the defects of the SEI film layer, the defects will gradually lead to the growth of metal filaments and dendrites, accelerating the poor consumption of electrolyte and the rapid decay of Coulombic efficiency. In order to stabilize the interface layer between the anode and the electrolyte, technicians have tried to enhance the SEI film layer with various electrolyte additives or new lithium current collectors. Although these strategies can improve the uniform deposition and cyclability of lithium metal batteries, the mechanical strength of the obtained SEI film layer is still not enough to inhibit dendrite growth.

[0004] To address these issues, researchers have explored numerous approaches to construct robust artificial SEI membranes to prevent dendrite growth during charge and discharge. For example, coating the anode of a lithium battery with inorganic materials (such as metal chloroperovskites and carbon materials) can shield the contact between metallic lithium and the liquid electrolyte, allowing lithium ions to shuttle rapidly at a low energy barrier. However, due to the fragile nature of inorganic artificial SEI membranes, they are prone to fracture when the volume of metallic lithium changes significantly. Alternatively, polymers with superior flexibility and high elasticity can be used to match dendrite growth to overcome the shortcomings of pure inorganic materials in designing artificial SEI membranes. However, artificial SEI membranes based on organic linear polymers with low mechanical modulus still have difficulty suppressing dendrite growth during long-term cycling, especially at high current densities (above 4C), which ultimately leads to battery cycle failure. To address the limitations of the aforementioned organic linear polymers or inorganic SEI membranes, organic-inorganic composite materials have been proposed as materials for artificial SEI membranes. However, the introduction of inorganic components increases the weight of the electrode and reduces the specific capacity of the battery. In addition, for most lithium-ion batteries using artificial SEI films, the current density and areal capacity loading of cycling tests are still less than 5 mA cm -2 and 3mAh cm -2 .

[0005] Therefore, it is urgent to solve the problem that the mechanical strength of the existing SEI film is not enough to inhibit dendrite growth and provide a SEI film material to construct an artificial SEI film with high mechanical modulus, good elasticity and high current density durability in the development of lithium-ion batteries. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides an artificial SEI material and its preparation method, an artificial SEI film, and an artificial SEI film-modified negative electrode, aiming to address the problem that the mechanical strength of the existing SEI film layer is insufficient to inhibit dendrite growth.

[0007] In a first aspect of the present invention, an artificial SEI material is provided. The artificial SEI material comprises an organic polymer brush formed by grafting cellulose nanofibers with polystyrene sulfonate.

[0008] According to the artificial SEI material of the embodiment of the present invention, there are at least the following beneficial effects: the artificial SEI material provided by the present invention is an organic polymer brush (CNF-g-PSSX) prepared by grafting polystyrene sulfonate onto cellulose nanofibers (CNF). The polymer brush prepared from CNF has a strong skeleton due to its crystalline structure; and the side chain of polystyrene sulfonate (PSSX) has abundant -SO3 functional groups, which cooperate with the cations in the sulfonate to provide a fast ion transport channel, which can achieve high current density cycling and ensure good interface contact to avoid shedding. Due to the special molecular topology and the synergistic effect of multiple components, the organic polymer brush (CNF-g-PSSX) prepared by the present invention can simultaneously obtain high mechanical strength, high ionic conductivity and low interface impedance when forming an artificial SEI film, and through the strong electrostatic repulsion between the negatively charged -SO3 group and the negatively charged lithium dendrite tip surface, it shows a significant inhibitory effect on the continued growth of dendrites. When the artificial SEI film prepared using this organic polymer brush is deposited on a silicon-based negative electrode material, it can improve the continuous growth of the SEI film caused by the intrinsic expansion of the silicon-based material during the cycle, enabling it to exhibit excellent cycle stability at ultra-high current density.

[0009] In some embodiments of the present invention, the cellulose nanofibers are grafted onto polystyrene sulfonate via surface-initiated atom transfer radical polymerization (SI-ATRP). SI-ATRP is a highly controllable surface modification method that uses surface-initiated atom transfer radical polymerization to chemically modify the surface of solid materials. The grafted polymer brush forms a polymer film of a specified structure on the solid surface through chemical bonds, thereby improving the material's properties.

[0010] In some embodiments of the present invention, the polystyrene sulfonate (PSSX) includes at least one of polystyrene sulfonate lithium (PSSLi) or polystyrene sulfonate sodium (PSSNa).

[0011] In some embodiments of the present invention, the artificial SEI material includes an organic polymer brush (CNF-g-PSSLi) formed by cellulose nanofibers (CNF) grafted with lithium polystyrene sulfonate (PSSLi), or an organic polymer brush (CNF-g-PSSNa) formed by cellulose nanofibers (CNF) grafted with sodium polystyrene sulfonate (PSSNa); preferably CNF-g-PSSLi.

[0012] The polymer brush (CNF-g-PSSLi) prepared from cellulose nanofibers (CNF) has a strong skeleton due to its crystalline structure. The lithium single-ion conductive PSSLi side chain has abundant -SO3 functional groups that cooperate with lithium ions, providing a fast ion transport channel, enabling high current density cycling, and ensuring good interfacial contact to avoid shedding. Due to the special molecular topology and the synergistic effect of multiple components, the CNF-g-PSSLi prepared by the present invention can simultaneously obtain high mechanical strength, high ionic conductivity and low interfacial impedance when forming an artificial SEI film. In addition, the strong electrostatic repulsion between the negatively charged -SO3 groups and the negatively charged lithium dendrite tip surface shows a significant inhibitory effect on the continued growth of dendrites. When the artificial SEI film prepared using the organic polymer brush CNF-g-PSSLi is deposited on a silicon-based negative electrode material, it can improve the continuous growth of the SEI film caused by the intrinsic expansion of the silicon-based material during the cycle, so that it exhibits excellent cycle stability at ultra-high current density.

[0013] In some embodiments of the present invention, the molar mass ratio of the cellulose nanofibers to the polystyrene sulfonate is 1:4 to 1:10, preferably 1:7.

[0014] In some embodiments of the present invention, the graft density of the polystyrene sulfonate is 5.0×10 -7 ~1.7×10 -6 mol / m 2 Within this range, the formation of continuous ion channels by polystyrene sulfonate can be ensured without sacrificing the rigidity of CNF.

[0015] Specifically, the graft density can be measured by thermogravimetric analysis. The thermal decomposition peak temperature (Td) and the residual carbon rate of the graft chain are positively correlated with the graft density, and the graft density can be indirectly reflected by the thermal decomposition behavior.

[0016] In a second aspect of the present invention, a method for preparing the above-mentioned artificial SEI material is provided, comprising the steps of:

[0017] S100, reacting cellulose nanofibers with a halogenated acyl compound to generate halogenated cellulose nanofibers (CNF-X);

[0018] S200, adding the halogenated cellulose nanofibers, styrene sulfonate, copper bromide, and tertiary amine ligands to an alcohol solution and mixing, then adding a reducing agent, and reacting at a predetermined temperature and for a predetermined time to generate a cellulose nanofiber grafted polystyrene sulfonate polymer brush to obtain the artificial SEI material.

[0019] The method for preparing an artificial SEI material according to an embodiment of the present invention has at least the following beneficial effects: The preparation method provided by the present invention uses surface-initiated atom transfer radical polymerization (SI-ATRP) technology to graft cellulose nanofibers (CNF) with polystyrene sulfonate (PSSX) to prepare an organic polymer brush (CNF-g-PSSX). The above-mentioned surface modification method is highly controllable and can chemically modify the surface of a solid material, graft the polymer brush, and form a polymer film of a specified structure on the solid surface through chemical bonds to improve the properties of the material. In addition, this method adopts a liquid phase method for preparation, which is simple in process and does not require harsh reaction conditions, and has the potential for large-scale application.

[0020] In some embodiments of the present invention, when the polystyrene sulfonate is lithium polystyrene sulfonate (PSSLi), the process further comprises the steps of:

[0021] S300, dialyzing the grafted polystyrene sulfonate into lithium polystyrene sulfonate in a lithium chloride (LiCl) solution.

[0022] In some embodiments of the present invention, the molar mass ratio of the cellulose nanofibers to the polystyrene sulfonate is 1:4 to 1:10, preferably 1:7.

[0023] In some embodiments of the present invention, the method for preparing the artificial SEI material includes at least one of (a1) to (a9):

[0024] (a1) grafting polystyrene sulfonate onto the cellulose nanofibers via surface-initiated atom transfer radical polymerization;

[0025] (a2) the halogenated acyl compound comprises at least one of an acyl bromide compound or an acyl chloride compound;

[0026] (a3) When (a2) is included, the acid bromide compound includes at least one of 2-bromoisobutyl bromide, 2-bromopropionyl bromide, 2-chloroisobutyryl bromide, or 2-bromoisobutyryl bromide;

[0027] (a4) When (a2) is included, the acid chloride compound includes p-chloromethylbenzoyl chloride;

[0028] (a5) the halogenated cellulose nanofibers (CNF-X) include at least one of cellulose nanofibers-bromine (CNF-Br) and cellulose nanofibers-chlorine (CNF-Cl);

[0029] (a6) the tertiary amine ligand comprises at least one of pentamethyldiethyltriamine, bipyridine, tetramethyldiethyltriamine, or tris(2-picolyl)amine;

[0030] (a7) the reducing agent comprises at least one of ascorbic acid (vitamin C, VC), sodium ascorbate, tin (II) 2-ethylhexanoate, glucose, a sulfite compound, or a metal reducing agent;

[0031] (a8) The predetermined time is 12 to 36 hours;

[0032] (a9) The predetermined temperature is 50 to 80°C.

[0033] In some embodiments of the present invention, the halogenated acyl compound includes at least one of an acyl bromide or an acyl chloride, but is not limited thereto and may also include other compounds containing active halogens and highly reactive groups. The core function of the halogenated acyl compound is to introduce ATRP initiation sites (halogen sites, such as -Br or -Cl) into the cellulose nanofibers, thereby constructing functionalized polymer brushes.

[0034] In some embodiments of the present invention, the tertiary amine ligand includes at least one of pentamethyldiethylenetriamine, bipyridine (bpy), tetramethyldiethylenetriamine (Me6TREN), or tris(2-picolyl)amine (TPMA), but is not limited thereto. The tertiary amine ligands belong to the polyamine class of ligands. These ligands coordinate with the metal center through the lone pair electrons of the nitrogen atom, forming the core of the ATRP catalytic system. In the process of preparing the artificial SEI membrane, they serve as catalytic ligands, and their core function is to improve the controllability and efficiency of the polymerization reaction.

[0035] In some embodiments of the present invention, the alcohol solution comprises at least one of methanol or ethanol.

[0036] In some embodiments of the present invention, the reducing agent comprises at least one of ascorbic acid, sodium ascorbate, tin(II) 2-ethylhexanoate, glucose, a sulfite compound, or a metal reducing agent. The reducing agent functions to reduce Cu(II) to catalytically active Cu(I), thereby initiating and maintaining the ATRP reaction (regenerating the catalytically active species).

[0037] In some embodiments of the present invention, the predetermined time is 12 to 36 hours, preferably 24 hours.

[0038] In some embodiments of the present invention, the predetermined temperature is 50-80°C, preferably 60°C.

[0039] In some embodiments of the present invention, the graft density of the polystyrene sulfonate is 5.0×10 -7 ~1.7×10 -6 mol / m 2Within this range, the formation of continuous ion channels by polystyrene sulfonate can be ensured without sacrificing the rigidity of CNF.

[0040] Specifically, the graft density can be measured by thermogravimetric analysis. The thermal decomposition peak temperature (Td) and the residual carbon rate of the graft chain are positively correlated with the graft density, and the graft density can be indirectly reflected by the thermal decomposition behavior.

[0041] In some specific embodiments of the present invention, the artificial SEI material is an organic polymer brush (CNF-g-PSSLi) formed by grafting cellulose nanofibers (CNF) with lithium polystyrene sulfonate (PSSLi), and the preparation method comprises the following steps:

[0042] Cellulose nanofibers (CNF) are reacted with 2-bromoisobutyl bromide to generate cellulose nanofiber-bromine; the cellulose nanofiber-bromine, sodium p-styrene sulfonate, copper bromide, and pentamethyldiethylenetriamine are added to an alcohol solution and mixed, and then ascorbic acid is added. The mixture is reacted at 50-80°C for 12-36 hours to generate a cellulose nanofiber-grafted sodium polystyrene sulfonate polymer brush (CNF-g-PSSNa); the grafted sodium polystyrene sulfonate is converted into lithium polystyrene sulfonate by dialysis in a lithium chloride (LiCl) solution to obtain an organic polymer brush CNF-g-PSSLi.

[0043] In some embodiments of the present invention, the graft density of lithium polystyrene sulfonate is 5.0×10 -7 ~1.7×10 -6 mol / m 2 Within this range, the formation of continuous ion channels by lithium polystyrene sulfonate can be ensured without sacrificing the rigidity of CNF.

[0044] In some specific embodiments of the present invention, the artificial SEI material is an organic polymer brush (CNF-g-PSSNa) formed by grafting cellulose nanofibers (CNF) with sodium polystyrene sulfonate (PSSNa), and the preparation method comprises the following steps:

[0045] Cellulose nanofibers (CNF) are reacted with 2-bromoisobutyl bromide to generate cellulose nanofiber-bromine; the cellulose nanofiber-bromine, sodium p-styrene sulfonate, copper bromide, and pentamethyldiethylenetriamine are added to an alcohol solution and mixed, and then ascorbic acid is added. The mixture is reacted at 50-80°C for 12-36 hours to generate a cellulose nanofiber-grafted sodium polystyrene sulfonate polymer brush (CNF-g-PSSNa).

[0046] In some embodiments of the present invention, the grafting density of sodium polystyrene sulfonate is 5.0×10 -7 ~1.7×10 -6 mol / m2 Within this range, the formation of continuous ion channels by sodium polystyrene sulfonate can be ensured without sacrificing the rigidity of CNF.

[0047] In some embodiments of the present invention, step S100 specifically includes:

[0048] S101, dispersing cellulose nanofibers (CNF) in deionized water, adding 0.01 M HCl to obtain a uniform CNF suspension;

[0049] S102, repeatedly centrifuging and redispersing the CNF suspension, and then redispersing it in N,N-dimethylformamide (DMF) to obtain a CNF / DMF dispersion;

[0050] S103, mixing the CNF / DMF dispersion and triethylamine (TEA) in a Schlenk flask, and purging with nitrogen to obtain a CNF / DMF / TEA mixture;

[0051] S104. 2-Bromoisobutyl bromide (BiBB) dissolved in DMF was slowly added to the CNF / DMF / TEA mixture under a nitrogen atmosphere at 0°C. The resulting mixed solution was stirred and reacted under a nitrogen atmosphere at 25°C. The generated product was thoroughly washed with an ethanol aqueous solution to obtain cellulose nanofiber-bromine (CNF-Br).

[0052] In some embodiments of the present invention, step S200 specifically includes:

[0053] S201, adding CNF-Br, p-styrenesulfonate, copper bromide (CuBr2), pentamethyldiethyltriamine, and alcohol solution into a Schlenk flask and mixing;

[0054] S202, purging the mixture with nitrogen for a period of time, and placing it in an oil bath for preheating;

[0055] S203, adding degassed ascorbic acid to the above mixture, storing at 30° C. for 1 hour, then heating at 50-80° C. for 12-36 hours, cooling to room temperature after the reaction is completed, and exposing to air to terminate the reaction;

[0056] S204 , washing and purifying the product by centrifugation with distilled water to obtain cellulose nanofiber grafted polystyrene sulfonate polymer brushes (CNF-g-PSSX), namely the artificial SEI material.

[0057] In a third aspect of the present invention, an artificial SEI film is provided, which is formed from the artificial SEI material described above or the artificial SEI material prepared by the preparation method described above.

[0058] Since the artificial SEI film adopts all the technical solutions of the artificial SEI material of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment. That is, the artificial SEI film can simultaneously obtain high mechanical strength, high ionic conductivity and low interfacial impedance, and through the strong electrostatic repulsion between the negatively charged -SO3 groups in the artificial SEI material and the negatively charged surface of the lithium dendrite tip, it shows a significant inhibitory effect on the continued growth of dendrites. When this artificial SEI film is deposited on a silicon-based negative electrode material, it can improve the continuous growth of the SEI film caused by the intrinsic expansion of the silicon-based material during the cycle process, so that it exhibits excellent cycle stability at ultra-high current density.

[0059] In the fourth aspect of the present invention, an artificial SEI film-modified negative electrode is proposed, comprising a negative electrode current collector and an artificial SEI film-modified negative electrode material coated on at least one side of the negative electrode current collector, wherein the artificial SEI film-modified negative electrode material comprises a substrate and an artificial SEI film as described above composited on the surface of the substrate.

[0060] Since the artificial SEI film-modified negative electrode adopts all the technical solutions of the artificial SEI material and artificial SEI film of the above-mentioned embodiment, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiment. That is, the artificial SEI film is deposited on the artificial SEI film modified negative electrode, and the artificial SEI film can simultaneously obtain high mechanical strength, high ionic conductivity and low interfacial impedance, and through the strong electrostatic repulsion between the negatively charged -SO3 groups in the artificial SEI material and the negatively charged lithium dendrite tip surface, it shows a significant inhibitory effect on the continuous growth of dendrites. Therefore, the artificial SEI film-modified negative electrode can improve the continuous growth of SEI film caused by the intrinsic expansion of silicon-based materials during the cycle process, so that it exhibits excellent cycle stability at ultra-high current density.

[0061] In some embodiments of the present invention, the thickness of the artificial SEI film is 5 to 9 nm.

[0062] In some embodiments of the present invention, the negative electrode current collector substrate includes at least one of copper foil and composite copper foil.

[0063] In some embodiments of the present invention, the substrate comprises at least one of graphite or silicon-based materials.

[0064] Specifically, the graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite.

[0065] Specifically, the silicon-based material can be selected from one or more of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys, or a mixture of silicon negative electrode materials and other commonly used negative electrode active materials. The other negative electrode active materials include but are not limited to one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microbeads, tin-based materials, lithium titanate, or other metals that can form alloys with lithium.

[0066] In some preferred embodiments of the present invention, the silicon-based material includes silicon-carbon (Si—C) material and silicon-oxygen (Si—O) material.

[0067] In some specific embodiments of the present invention, the artificial SEI film-modified negative electrode material further includes a negative electrode conductor and a negative electrode binder.

[0068] Specifically, the negative electrode conductive agent includes at least one of acetylene black, graphene, graphyne, carbon nanotubes, carbon fibers, and conductive carbon black. The present invention has no special requirements for the negative electrode conductive agent, and any conventional conductive agent in the art can be used.

[0069] Specifically, the negative electrode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), or polyacrylate (PAA). The present invention has no special requirements for the negative electrode binder, and any conventional binder in the art can be used.

[0070] In a fifth aspect of the present invention, a method for preparing an artificial SEI film-modified negative electrode is provided, comprising the steps of:

[0071] S10, dispersing the artificial SEI material or the artificial SEI material prepared by the above-mentioned preparation method into an organic solvent to form an artificial SEI material dispersion;

[0072] S20, immersing a substrate in the artificial SEI material dispersion to react, or uniformly coating the artificial SEI material dispersion on the surface of the substrate, then removing the organic solvent, and forming a film of the artificial SEI material on the surface of the substrate to obtain an artificial SEI film-modified negative electrode material;

[0073] S30, coating the artificial SEI film-modified negative electrode material on a negative electrode current collector to obtain an artificial SEI film-modified negative electrode.

[0074] In some embodiments of the present invention, the organic solvent is dimethyl sulfoxide (DMSO).

[0075] In some embodiments of the present invention, the substrate is immersed in the artificial SEI material dispersion, heated to 50° C. and stirred for 3 hours to react.

[0076] In some embodiments of the present invention, the negative electrode current collector substrate includes at least one of copper foil and composite copper foil.

[0077] In some embodiments of the present invention, the substrate comprises at least one of graphite or silicon-based materials.

[0078] Specifically, the graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite.

[0079] Specifically, the silicon-based material can be selected from one or more of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys, or a mixture of silicon negative electrode materials and other commonly used negative electrode active materials. The other negative electrode active materials include but are not limited to one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microbeads, tin-based materials, lithium titanate, or other metals that can form alloys with lithium.

[0080] In some preferred embodiments of the present invention, the silicon-based material includes silicon-carbon (Si—C) material and silicon-oxygen (Si—O) material.

[0081] In some embodiments of the present invention, in the artificial SEI film-modified negative electrode, the thickness of the artificial SEI film is 5 to 9 nm.

[0082] In a sixth aspect of the present invention, a lithium-ion battery is provided, comprising the above-mentioned artificial SEI film-modified negative electrode or the artificial SEI film-modified negative electrode prepared by the above-mentioned preparation method.

[0083] Since the lithium-ion battery adopts all the technical solutions of the artificial SEI film-modified negative electrode of the above embodiment, it has at least all the beneficial effects brought about by the technical solutions of the above embodiment. That is, the artificial SEI film is deposited on the artificial SEI film-modified negative electrode, and the artificial SEI film can simultaneously obtain high mechanical strength, high ionic conductivity and low interfacial impedance, and through the strong electrostatic repulsion between the negatively charged -SO3 groups in the artificial SEI material and the negatively charged lithium dendrite tip surface, it shows a significant inhibitory effect on the continued growth of dendrites. Therefore, the above lithium-ion battery can improve the continuous growth of the SEI film caused by the intrinsic expansion of the silicon-based material during the cycle process, so that it exhibits excellent cycle stability at ultra-high current density.

[0084] In some embodiments of the present invention, the lithium-ion battery further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on at least one side of the surface of the positive electrode current collector.

[0085] In some specific embodiments of the present invention, the positive electrode current collector includes at least one of aluminum foil and composite aluminum foil.

[0086] In some specific embodiments of the present invention, the raw materials of the positive electrode active material layer include a positive electrode active material, a positive electrode conductor and a positive electrode binder.

[0087] In the present invention, the positive electrode active material is a positive electrode active material commonly used in lithium ion batteries, including but not limited to chemical formulas such as Li x Ni h Co y M z O 2-d N d (wherein 0.95≤x≤1.2, h>0, y≥0, z≥0, and h+y+z=1, 0≤d≤1, M is selected from a combination of one or more of Mn and Al, and N is selected from a combination of one or more of F, P, and S), the positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active material may be a combination of one or more of: O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc. The positive electrode active material may also be subjected to a modification treatment. Methods for modifying the positive electrode active material should be known to those skilled in the art. For example, the positive electrode active material may be modified by coating, doping, etc. The materials used for the modification treatment may include, but are not limited to, a combination of one or more of: Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc.

[0088] The positive electrode conductive agent includes at least one of acetylene black, graphene, graphyne, carbon nanotubes, carbon fibers, and conductive carbon black. The present invention has no special requirements for the positive electrode conductive agent, and conventional conductive agents in the field can be used.

[0089] The positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), or polyacrylate (PAA). The present invention has no special requirements for the positive electrode binder, and any conventional binder in the art can be used.

[0090] In some embodiments of the present invention, the lithium-ion battery further includes a separator spaced between the positive electrode sheet and the artificial SEI film-modified negative electrode.

[0091] In some embodiments of the present invention, the separator can be made of any material suitable for lithium-ion battery separators in the art, such as, but not limited to, polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. In actual production, the material and structure of the separator are not strictly limited. For example, the separator can be a multilayer structure formed by stacking the above materials, a single layer structure formed by mixing the above materials, or a single layer structure formed by a single material; as long as it can perform the basic function of a separator, it can be used.

[0092] In some embodiments of the present invention, the lithium-ion battery further comprises an electrolyte, which infiltrates the positive electrode, the artificial SEI-modified negative electrode, and the separator. The electrolyte comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt may be LiPF6 and / or LiBOB, as used in high-temperature electrolytes; at least one of LiBF4, LiBOB, and LiPF6, as used in low-temperature electrolytes; at least one of LiBF4, LiBOB, LiPF6, and LiTFSI, as used in overcharge-preventing electrolytes; or at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent may be a cyclic carbonate, including PC and EC; a chain carbonate, including DEC, DMC, or EMC; or a carboxylic acid ester, including PP, MA, EA, and EP. The additives include but are not limited to at least one of film-forming additives, conductive additives, flame retardant additives, overcharge prevention additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and water-based safety additives.

[0093] In some embodiments of the present invention, the present invention further provides a secondary battery comprising the aforementioned artificial SEI membrane-modified negative electrode. The artificial SEI membrane-modified negative electrode provided by the present invention can be applied not only to the aforementioned lithium-ion battery, but also to other secondary batteries, including sodium-ion batteries, potassium-ion batteries, and the like, without limitation.

[0094] In a seventh aspect of the present invention, a use of the above-mentioned lithium-ion battery in an energy storage device, an electrical device or an electronic device is proposed. BRIEF DESCRIPTION OF THE DRAWINGS

[0095] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0096] Figure 1 Schematic diagram of the SEI-coated surface morphology of the artificial SEI film-modified negative electrode material provided in Example 3 of the present invention;

[0097] Figure 2 Schematic diagram of the SEI coating micromorphology of the artificial SEI film modified negative electrode material provided in Example 3 of the present invention. DETAILED DESCRIPTION

[0098] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0099] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0100] In the description of the present invention, unless otherwise indicated, the numerical range "a-b" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. Unless otherwise indicated, the individual reactions or steps may or may not be performed sequentially. Preferably, the reaction methods of the present invention are performed sequentially.

[0101] If no specific techniques or conditions are specified in the following examples, the methods were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments without manufacturer specified are commercially available conventional products.

[0102] Example 1

[0103] This embodiment provides an artificial SEI material, which is prepared by grafting poly (lithium p-phenylene sulfonate) (PSSLi) onto cellulose nanofibers (CNF) through surface-initiated atom transfer radical polymerization (SI-ATRP), namely, an organic polymer brush CNF-g-PSSLi.

[0104] The preparation steps are:

[0105] (1) Preparation of CNF-Br:

[0106] 0.5 g of CNF was dispersed in 50 mL of distilled water, and 0.2 mL of 0.01 M HCl was added to obtain a uniform CNF suspension. The CNF suspension was centrifuged repeatedly (8000 rpm, 10 min) for 6 times and then dispersed in N,N-dimethylformamide (DMF) to obtain a CNF / DMF dispersion.

[0107] 30 mL of a CNF / DMF dispersion with a concentration of 16.7 mg / mL was mixed with 3.56 g of triethylamine (TEA) in a 50 mL Schlenk flask and purged with nitrogen for 30 min to obtain a CNF / DMF / TEA mixture.

[0108] 3.22 g of 2-bromoisobutyl bromide (BiBB) dissolved in 20 mL of DMF was slowly added to the CNF / DMF / TEA mixture at 0°C under a nitrogen atmosphere. Subsequently, the mixed solution was stirred at 25°C under a nitrogen atmosphere for 24 h. After the reaction was completed, the product CNF-Br was thoroughly washed with an ethanol aqueous solution (water / ethanol = 1:1 by volume).

[0109] (2) Preparation of CNF-g-PSSNa:

[0110] 0.9 g CNF-Br, 8.24 g sodium p-styrenesulfonate, 17.8 mg CuBr2, 0.138 g pentamethyldiethylenetriamine, and 20 mL methanol were added to a 100 mL Schlenk flask. The mixture was purged with nitrogen for 30 minutes and preheated in an oil bath at 30°C. Degassed ascorbic acid (140 mg) was then added to the mixture, which was stored at 30°C for 1 hour, heated at 60°C for 24 hours, cooled to room temperature, and terminated by exposure to air. The resulting product was purified by centrifugation and washing with distilled water several times to obtain the polymer brush CNF-g-PSSNa.

[0111] (3) Preparation of CNF-g-PSSLi:

[0112] The polymer brush CNF-g-PSSNa was sealed in a dialysis bag (Mw = 3500) and then immersed in a 2M LiCl solution for dialysis to convert the PSSNa chains into PSSLi chains. The obtained CNF-g-PSSLi polymer brush was then separated by centrifugation cycle and finally freeze-dried to obtain the product.

[0113] Example 2

[0114] This embodiment provides an artificial SEI material, which is prepared by grafting poly (sodium p-phenylene sulfonate) (PSSNa) onto cellulose nanofibers (CNF) through surface-initiated atom transfer radical polymerization (SI-ATRP), namely, an organic polymer brush CNF-g-PSSNa.

[0115] The preparation steps are:

[0116] (1) Preparation of CNF-Br:

[0117] 0.5 g of CNF was dispersed in 50 mL of distilled water, and 0.2 mL of 0.01 M HCl was added to obtain a uniform CNF suspension. The CNF suspension was centrifuged repeatedly (8000 rpm, 10 min) for 6 times and then dispersed in N,N-dimethylformamide (DMF) to obtain a CNF / DMF dispersion.

[0118] 30 mL of a CNF / DMF dispersion with a concentration of 16.7 mg / mL was mixed with 3.56 g of triethylamine (TEA) in a 50 mL Schlenk flask and purged with nitrogen for 30 min to obtain a CNF / DMF / TEA mixture.

[0119] 3.22 g of 2-bromoisobutyl bromide (BiBB) dissolved in 20 mL of DMF was slowly added to the CNF / DMF / TEA mixture at 0°C under a nitrogen atmosphere. Subsequently, the mixed solution was stirred at 25°C under a nitrogen atmosphere for 24 h. After the reaction was completed, the product CNF-Br was thoroughly washed with an ethanol aqueous solution (water / ethanol = 1:1 by volume).

[0120] (2) Preparation of CNF-g-PSSNa:

[0121] 0.9 g CNF-Br, 8.24 g sodium p-styrenesulfonate, 17.8 mg CuBr2, 0.138 g pentamethyldiethylenetriamine, and 20 mL methanol were added to a 100 mL Schlenk flask. The mixture was purged with nitrogen for 30 minutes and preheated in an oil bath at 30°C. Degassed ascorbic acid (140 mg) was then added to the mixture, which was stored at 30°C for 1 hour, heated at 60°C for 24 hours, cooled to room temperature, and terminated by exposure to air. The resulting product was purified by centrifugation and washing with distilled water several times to obtain the polymer brush CNF-g-PSSNa.

[0122] Example 3

[0123] This embodiment provides an artificial SEI film-modified negative electrode material, which is formed by compounding an artificial SEI film on the surface of a silicon-carbon negative electrode material.

[0124] In order to form a uniform artificial SEI film on the surface of the silicon-carbon negative electrode material, the CNF-g-PSSLi polymer brush prepared in Example 1 was first dispersed in dimethyl sulfoxide (DMSO) with a concentration of 5 mg / mL; then, in a glove box, the silicon-carbon negative electrode material was placed in the above solution for infiltration, heated to 50°C and stirred for 3 hours; finally, it was dried by forced air at 80°C to evaporate the solvent. CNF-g-PSSLi will form a uniform film on the surface of the silicon-carbon particles, thus obtaining an artificial SEI film-modified negative electrode material, which is labeled as CNF-g-PSSLi@Si / C.

[0125] The main components of the SEI film in this embodiment are CNF:PSSLi, with a molar mass ratio of 1:7. The SEI-coated surface morphology and micromorphology of the artificial SEI film modified negative electrode material are as follows: Figure 1-2 ,Depend on Figure 1-2 It can be seen that SEI is deposited evenly and forms a uniform film on the surface of the substrate.

[0126] Example 4

[0127] The difference from Example 3 is that the CNF-g-PSSNa polymer brush prepared in Example 2 is used to form an artificial SEI film on the surface of the silicon-carbon negative electrode material, and the obtained artificial SEI film-modified negative electrode material is marked as CNF-g-PSSNa@Si / C.

[0128] The rest is the same as in Example 3 and will not be described again here.

[0129] Example 5

[0130] The difference from Example 3 is that the CNF-g-PSSLi polymer brush prepared in Example 1 is used to form an artificial SEI film on the surface of the silicon oxide negative electrode material, and the obtained artificial SEI film modified negative electrode material is marked as CNF-g-PSSLi@Si / O.

[0131] The rest is the same as in Example 3 and will not be described again here.

[0132] Example 6

[0133] This embodiment provides a micro half-cell, using the CNF-g-PSSLi@Si / C prepared in Example 3 as the negative electrode material, and preparing a slurry with a negative electrode material: Super P:CMC:SBR mass percentage = 80:10:4:6. The slurry is coated on a copper foil and dried at 80°C. A diaphragm (conventional ceramic coating diaphragm) is used as the electrolyte and Li is used as the metal anode to prepare a button battery.

[0134] Example 7

[0135] The difference from Example 6 is that the button battery is prepared by using the CNF-g-PSSNa@Si / C prepared in Example 4 as the negative electrode material.

[0136] The rest is the same as Example 6 and will not be repeated here.

[0137] Example 8

[0138] The difference from Example 6 is that the button battery is prepared by using the CNF-g-PSSLi@Si / O prepared in Example 5 as the negative electrode material.

[0139] The rest is the same as Example 6 and will not be repeated here.

[0140] Example 9

[0141] This embodiment provides a lithium-ion full battery, using the CNF-g-PSSLi@Si / C prepared in Example 3 as the negative electrode material, and preparing a negative electrode plate by mixing the above-mentioned negative electrode material and graphite in a ratio of 6:94. The prepared negative electrode plate is evenly mixed with carboxymethyl cellulose and a binder (styrene-butadiene rubber SBR) in a ratio of 90:7:3, and the plate is evenly coated and rolled on a copper foil to prepare a plate. The coating surface density is 0.101 / 1540.25g / mm 2 . After that, it was wound with the positive electrode sheet (lithium cobalt oxide, purchased from Tianjin Bamo) and the separator (Jie Li ceramic oil-based separator) to form a bare battery cell, which was then encapsulated with aluminum-plastic film and vacuum dried at 80°C. After the water content reached the standard, the lithium-ion battery electrolyte was injected. The electrolyte formula is: ethylene carbonate (EC) 14.3wt%, propylene carbonate (PC) 14.3wt%, diethyl carbonate (DEC) 21.45wt%, propyl propionate (PP) 21.45wt%, LiPF6 15wt%, fluoroethylene carbonate (FEC) 8wt%, 1,3-propane sultone (PS) 2.5wt%, adiponitrile (ADN) 1wt%, hexane tricarbonitrile (HTCN) 1.5wt%, ethylene glycol bis(propionitrile) ether (EGBE) 1wt%. After that, the battery is vacuum packaged and goes through the steps of standing, hot and cold pressing, forming, liquid extraction, volume separation, aging and the like (all of which are conventional technologies) to prepare a lithium-ion battery.

[0142] Example 10

[0143] The difference from Example 9 is that the lithium ion battery is prepared by using the CNF-g-PSSNa@Si / C prepared in Example 4 as the negative electrode material.

[0144] The rest is the same as Example 10 and will not be repeated here.

[0145] Example 11

[0146] The difference from Example 9 is that the lithium ion battery is prepared by using the CNF-g-PSSLi@Si / O prepared in Example 5 as the negative electrode material.

[0147] The rest is the same as Example 9 and will not be described again here.

[0148] Comparative Example 1

[0149] This embodiment provides a PSSLi-modified negative electrode material. The difference from Example 3 is that lithium polystyrene sulfonate (PSSLi) does not undergo in-situ grafting reaction with CNF-Br, and PSSLi is directly compounded on the surface of the silicon-carbon negative electrode material to form an artificial SEI film.

[0150] The preparation steps are:

[0151] (1) Sodium polystyrene sulfonate (PSSNa) was sealed in a dialysis bag (Mw = 3500) and then dialyzed in a 2M LiCl solution at 60°C with stirring and the solution changed every 4 hours. The dialysis bag was then immersed in distilled water, which was changed every 8 hours. After three changes of water, the target polystyrene lithium sulfonate (PSSLi) was obtained by freeze-drying.

[0152] (2) The prepared PSSLi was dispersed in dimethyl sulfoxide (DMSO) with a concentration of 5 mg / mL; then, in a glove box, the silicon-carbon negative electrode material was placed in the above solution for infiltration, heated to 50°C and stirred for 3 h; finally, it was dried under blast air at 80°C to evaporate the solvent, and PSSLi formed a film on the surface of the silicon-carbon particles, thus obtaining a PSSLi-modified negative electrode material, which was labeled as PSSLi@Si / C.

[0153] Comparative Example 2

[0154] This example provides an artificial SEI membrane-modified anode material, formed by compositely bonding an artificial SEI membrane to the surface of a silicon-carbon anode material. The artificial SEI membrane is made of graphene oxide (GO) sheets grafted with hairy lithium polystyrene sulfonate (PSSLi) chains on both sides. (Except for the substitution of GO for CNF, the remaining preparation steps are identical to those of Example 1.)

[0155] The prepared GO-g-PSSLi polymer brushes were dispersed in dimethyl sulfoxide (DMSO) with a concentration of 5 mg / mL. Then, in a glove box, the silicon-carbon anode material was placed in the above solution for infiltration, heated to 50°C and stirred for 3 hours. Finally, the solution was dried with forced air at 80°C to evaporate the solvent, allowing GO-g-PSSLi to form a film on the surface of the silicon-carbon particles, thus obtaining an artificial SEI film-modified anode material, labeled GO-g-PSSLi@Si / C.

[0156] Comparative Example 3

[0157] The difference between this comparative example and Example 3 is that the main components of the SEI film in this example are CNF:PSSLi, and the molar mass ratio is 1:3.

[0158] The rest is the same as in Example 3 and will not be described again here.

[0159] Comparative Example 4

[0160] This embodiment provides a micro half-cell, which uses the PSSLi modified negative electrode material prepared in Comparative Example 1 as the negative electrode material. The rest of the preparation method is the same as that in Example 6 and will not be repeated here.

[0161] Comparative Example 5

[0162] This embodiment provides a micro half-cell, using the GO-g-PSSLi@Si / C prepared in Comparative Example 2 as the negative electrode material. The rest of the preparation method is the same as that in Example 6 and will not be repeated here.

[0163] Comparative Example 6

[0164] This embodiment provides a lithium-ion full battery, using the PSSLi-modified negative electrode material prepared in Comparative Example 1 as the negative electrode material. The rest of the preparation method is the same as that in Example 9 and will not be repeated here.

[0165] Comparative Example 7

[0166] This embodiment provides a lithium-ion full battery, using the GO-g-PSSLi@Si / C prepared in Comparative Example 2 as the negative electrode material. The rest of the preparation method is the same as that in Example 9 and will not be repeated here.

[0167] Test Example 1

[0168] SEI characteristic tests were performed on the negative electrode materials of Examples 3-5 and Comparative Examples 1-2, respectively, using the following test methods:

[0169] Elastic modulus test: Fix the material between two fulcrums, apply a load to bend it, measure the strain caused by the bending, and calculate the elastic modulus;

[0170] SEI layer thickness: The thickness of the SEI interface was measured using a scanning electron microscope;

[0171] Interfacial resistance: Electrochemical impedance spectroscopy (EIS) can be used to study the kinetics of the electrode. -2 ~10 5 The test was performed in the hz frequency range with an amplitude of 5mV.

[0172] The electrochemical impedance spectroscopy (EIS) test of lithium-ion batteries was performed using a Zahner electrochemical workstation. First, select the EIS mode, enter the parameter setting interface, select different modes of impedance testing, and set the test frequency range (10 -2 ~10 5 hz), starting frequency point, frequency test sequence, sampling interval, etc. to get the test results.

[0173] The impedance spectrum is then fitted to the equivalent circuit (EIS) using Zsimpwin fitting software. First, open the impedance spectrum to be fitted, select the Nyquist graphical representation, and click the "Model Circuit" icon to create an equivalent circuit model. Click "Add" to add the required circuit components and connect them using connection points. Then, provide a frequency range to generate a simulation plot. After simulation, open the simulation plot in the graphics window. To fit the simulated spectrum to the measured EIS spectrum, select "Original," then "Simulate," and click "Fit." Finally, save and export the fitted data.

[0174] Current density: measured using an electrochemical impedance spectroscopy (EIS) instrument.

[0175] The test results are shown in Table 1.

[0176] Table 1

[0177] elastic modulus SEI layer thickness <![CDATA[Current density / (mA cm -2 )]]> Interface resistance Example 3 5.3GPa 5nm 20 9.8Ω Example 4 4.8Gpa 6nm 15 13.1Ω Example 5 5.3Gpa 9nm 8 13.6Ω Comparative Example 1 0.03Gpa 3μm 3 25.1Ω Comparative Example 2 2.6Gpa 1μm 10 20.2Ω

[0178] As can be seen from Table 1, the artificial SEI film prepared by the artificial SEI material of the present invention can still ensure an elastic modulus of up to 5.3 GPa when the thickness of the SEI layer reaches 5 nm, and the current density reaches 20 mA cm -2 The above shows that the material prepared by the scheme of the present invention has high mechanical strength and high dynamic performance. After being converted into PSSLi chain and compounded with silicon carbon material, Example 4 can still ensure 4.8Gpa strength and 15mAcm -2 The current density of the material obtained in Comparative Example 1 without in-situ grafting reaction with CNF-Br to regulate the skeleton was only 0.03GPa, and the current density was reduced to 3mA cm -2 , its mechanical and dynamic properties are significantly reduced.

[0179] Test Example 2

[0180] The lithium-ion full batteries of Examples 9-11 and Comparative Examples 6-7 were tested respectively, and the testing methods were:

[0181] Pressure resistance test: The material first-efficiency half-cell test is carried out with a compaction density gradient of 0.2, and the calculated value is the percentage of first-efficiency reduction.

[0182] Charging window: Directly charge to 4.53V at different rates, then discharge to 3.0V and observe the lithium deposition on the interface.

[0183] Swelling: The initial 50% SOC thickness of the battery cell test is H1, and the thickness of the 100% SOC test after cycling is H2. Swelling = (H2-H1) / H1.

[0184] The test results are shown in Table 2

[0185] Table 2

[0186] Pressure resistance Charging window Cycle times Swelling Example 9 0.5％ 3.5C no lithium precipitation 1500 13.5％ Example 10 1％ 3.5C no lithium precipitation 1200 15％ Example 11 0.8％ 3.2C no lithium precipitation 1000 14.5％ Comparative Example 6 4％ 3.0C lithium plating 1000 20％ Comparative Example 7 2％ 2.8C lithium deposition 1000 16.7％

[0187] As can be seen from Table 2, when the composite artificial SEI material of the present invention is used to prepare the negative electrode material of a lithium-ion battery, the pressure resistance is as low as 0.5%, the rate can reach 3.5C without lithium precipitation, and after 1500 cycles, the Swelling is maintained at 13.5%. The above shows that the artificial SEI material prepared by the present invention has high mechanical strength and high dynamic performance, which can ensure the performance of the battery cell in the full-electric battery. However, the composite artificial SEI material prepared in Example 1 not only has reduced pressure resistance and poor rate performance, but also expands to 20% after 1000 cycles, and the inhibitory effect on material expansion is significantly reduced. This shows that the material prepared by the present invention has good electronic conductivity, effectively improves the electron transfer rate of the material, and has a high coulombic efficiency; at the same time, having a high mechanical strength can effectively limit the volume expansion effect of silicon, so that it has good cycle stability.

[0188] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. An artificial SEI material, characterized in that: The artificial SEI material includes an organic polymer brush formed by grafting cellulose nanofibers with polystyrene sulfonate.

2. The artificial SEI material according to claim 1, characterized in that The polystyrene sulfonate comprises at least one of lithium polystyrene sulfonate or sodium polystyrene sulfonate; And / or, the molar mass ratio of the cellulose nanofibers to the polystyrene sulfonate is 1:4 to 1:

10.

3. A method for preparing the artificial SEI material according to any one of claims 1 to 2, characterized in that: The method comprises the steps of: reacting cellulose nanofibers with a halogenated acyl compound to generate halogenated cellulose nanofibers; The halogenated cellulose nanofibers, styrene sulfonate, copper bromide, and tertiary amine ligands are added to an alcohol solution and mixed, and then a reducing agent is added. After reacting at a predetermined temperature and for a predetermined time, a cellulose nanofiber grafted polystyrene sulfonate polymer brush is generated to obtain the artificial SEI material.

4. The method for preparing an artificial SEI material according to claim 3, wherein: The method comprises at least one of (a1) to (a9): (a1) the cellulose nanofibers are grafted with polystyrene sulfonate by surface-initiated atom transfer radical polymerization; (a2) the halogenated acyl compound comprises at least one of an acyl bromide compound or an acyl chloride compound; (a3) When (a2) is included, the acid bromide compound includes at least one of 2-bromoisobutyl bromide, 2-bromopropionyl bromide, 2-chloroisobutyryl bromide, or 2-bromoisobutyryl bromide; (a4) When (a2) is included, the acid chloride compound includes p-chloromethylbenzoyl chloride; (a5) the halogenated cellulose nanofibers include at least one of cellulose nanofibers-bromine or cellulose nanofibers-chloride; (a6) the tertiary amine ligands include at least one of pentamethyldiethylenetriamine, bipyridine, tetramethyldiethylenetriamine, or tris(2-picolyl)amine; (a7) the reducing agent comprises at least one of ascorbic acid, sodium ascorbate, tin(II) 2-ethylhexanoate, glucose, a sulfite compound, or a metal reducing agent; (a8) The predetermined time is 12 to 36 hours; (a9) The predetermined temperature is 50 to 80°C.

5. An artificial SEI film, characterized in that The film is obtained by forming the artificial SEI material according to any one of claims 1-2 or the artificial SEI material prepared by the preparation method according to any one of claims 3-4.

6. An artificial SEI film modified negative electrode, characterized in that: The invention comprises a negative electrode current collector and an artificial SEI film-modified negative electrode material coated on at least one side of the negative electrode current collector, wherein the artificial SEI film-modified negative electrode material comprises a substrate and the artificial SEI film according to claim 5 composited on the surface of the substrate.

7. The artificial SEI film modified negative electrode according to claim 6, characterized in that: The thickness of the artificial SEI film is 5-9 nm; and / or the substrate includes at least one of graphite and silicon-based materials.

8. A method for preparing an artificial SEI film-modified negative electrode, characterized in that: Including steps: Dispersing the artificial SEI material according to any one of claims 1 to 2 or the artificial SEI material prepared by the preparation method according to any one of claims 3 to 4 into an organic solvent to form an artificial SEI material dispersion; Immersing a substrate in the artificial SEI material dispersion to react, or uniformly coating the artificial SEI material dispersion on the surface of the substrate, then removing the organic solvent, and forming a film of the artificial SEI material on the surface of the substrate to obtain an artificial SEI film-modified negative electrode material; The artificial SEI film modified negative electrode material is coated on a negative electrode current collector to obtain an artificial SEI film modified negative electrode.

9. A lithium-ion battery, characterized in that: It comprises the artificial SEI film modified negative electrode according to any one of claims 6-7 or the artificial SEI film modified negative electrode prepared by the preparation method according to claim 8.

10. Use of the lithium-ion battery according to claim 9 in an energy storage device, an electrical device or an electronic device.

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